The present invention relates to hermetic coatings for multichip modules and polymer film structures.
In one form of high density interconnect (HDI) circuit module, an adhesive-coated polymer film overlay having via openings covers a substrate which can support integrated circuit chips in chip wells. The polymer film provides an insulated layer upon which is deposited a metallization pattern for interconnection of substrate metallization and/or individual circuit chips through the vias. Methods for performing an HDI process using overlays are further described in Eichelberger et al., U.S. Pat. No. 4,783,695, issued Nov. 8, 1988, and in Eichelberger et al., U.S. Pat. No. 4,933,042, issued Jun. 12, 1990. Generally a plurality of polymer film overlays and metallization patterns are used.
In another form of circuit module fabrication, as described by Cole et al., U.S. Pat. No. 5,527,741, issued Jun. 18, 1996, a method for fabricating a circuit module includes using a flexible interconnect layer having patterned metallization on a base insulative layer and an outer insulative layer. At least one circuit chip having chip pads is attached to the base insulative layer and vias are formed in the outer and base insulative layers to expose selected portions of the base insulative layer metallization and the chip pads. A patterned outer metallization layer is applied over the outer insulative layer extending through selected ones of the vias to interconnect selected ones of the chip pads and selected portions of the base insulative layer metallization.
Modules fabricated using the above processes have improved reliability when effectively sealed. Conventional hermetic sealing teachings include welding, soldering, or glass-sealing a prefabricated hermetic lid to a package including the module. These processes are not conformal to the module and typically result in significant increases in packaging volume. Furthermore, when dielectric materials such as glass or ceramic are used as sealing materials, electrical input/output connections must be formed prior to sealing.
Neugebauer et al., U.S. Pat. No. 5,336,928, issued Aug. 9, 1994, describes a conformal hermetic barrier fabricated by depositing a continuous copper film and subsequently electroplating lead over the copper. The resulting conformal barrier requires a continuous metal layer and a plurality of electrical connections cannot easily be made though the hermetic layer.